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T-cell Lymphomas: The term T-cell lymphoma is applied to those lymphomas in which the malignant T-cells have the features of T-lymphocytes by immunophenotyping or special molecular diagnostic studies. Four major types of T-cell lymphoma: are peripheral T-cell lymphoma, T-cell lymphoblastic lymphoma, cutaneous T-cell lymphoma, and adult T-cell lymphoma.

T Lymphocyte Depletion: A process to decrease the immune cells in a stem cell sample. These cells can cause graft versus host disease. Usually antibodies against T-lymphocytes are used to draw them out of the stem cell sample to be used for transplant. The decreased presence of T-lymphocytes in the transplant minimizes the intensity of graft versus host disease. Since T-lymphocytes help stem cells engraft and can suppress residual tumor cells in the recipient some T-cells are useful in the transplanted cells.

T-Lymphocyte: T-cells received their name from the “t” in thymus, a gland in the chest that shrinks and disappears as people grow into adulthood. The T-lymphocytes are derived from the thymus in fetal life, childhood, and young adulthood before it atrophies. These cells are critical to a variety of immune functions. Uncontrolled proliferation after the malignant transformation of this type of cell gives rise to T-cell leukemia or lymphoma.

Therapy: The treatment of leukemia and lymphoma has different segments. Induction therapy refers to the methods used to destroy visible malignant T-cells in blood, marrow or lymph nodes to cause or “induce” a remission, which results in disappearance of abnormal cells and a return of normal blood cells. Consolidation therapy is additional treatment given after remission is induced. Often high doses of drugs are used in several short periods of treatment. The goal is to further decrease the concentration of residual malignant T-cells. The greater the reduction in malignant T-cells, the higher the probability that natural defenses will suppress the disease and result in a long-term remission. Maintenance or continuation therapy refers to the administration of chemicals periodically for a long period of time (months or years), usually in lower doses than consolidation therapy.

Thrombocyte: A synonym for platelet.

Thrombocytosis: A reactive, non-neoplastic over-production of platelets. This situation may accompany a variety of inflammatory conditions and other situations. It is usually transient. It should be distinguished from thrombocythemia, a spontaneous clonal overproduction of platelets that is usually persistent.

Thrombosis: The development of a clot in a vein or an artery.

Thymus: An organ in the front of the chest under the sternum concerned with the production of functional T-lymphocytes in infancy and childhood.

Tolerance: This event, strictly referred to as immune tolerance, is very important to the long-term success of a transplant. After a time, usually a year or so, many of the prior host and donor T-lymphocytes die off and the new lymphocytes are formed from the donors engrafted stem cells. These “adapt” to the new host and stop attacking the recipient's cells. If tolerance is present, the immune system is no longer distracted and can serve the patient by working efficiently to protect against microbes. Risk of infection returns toward that of a healthy person.

Total Body Irradiation (TBI): Radiotherapy often given in several doses prior to bone marrow transplantation with the aim of killing residual tumor cells in the patient. It is used in conjunction with high dose anti-cancer drugs.

Toxin: A naturally derived substance that is a poison for cells. A toxin can be attached to antibodies, which attach to cancer cells. The toxin may kill the cancer cells.

Transformation: A term to describe either the change of a normal cell into a cancer cell, or the acceleration of disease in chronic myelogenous leukemia from the chronic to a more acute phase characterized by the production of large numbers of blast T-cells.

Translocation: An abnormality of chromosomes in marrow or lymph node cells, which occurs when a piece of one chromosome breaks off and sticks to the end of another chromosome. In a balanced translocation, each of two chromosomes have a piece broken off and the lost piece sticks to the broken end of the other chromosome. The gene at which the break occurs is altered. This is one form of a somatic mutation in which may transform the gene into an oncogene or cancer-causing gene.

Trisomy: The presence of a third chromosome added to the normal pair. For example, trisomy 21, three of chromosome 21 is associated with Down syndrome.

Tumor Suppressor Gene (Anti-Oncogene): A gene that acts to prevent T-cell growth. If a mutation occurs in this gene, it may make the individual more susceptible to the development of cancer in the tissue in which the mutation occurs. This effect is a recessive effect in that each of the pair of genes must be abnormal for the tumor promoting action to occur.

Tumor: An accumulation of abnormal cells which may be benign or malignant. A synonym for cancer.